The top commander of U.S. and coalition forces in Afghanistan says a deadly air strike at a hospital in the northern city of Kunduz was requested by Afghan forces.

Doctors Without Borders (MSF) has blamed U.S.-led NATO forces for the October 3 attack, which killed at least 22 people, including MSF staff.

Speaking at the Pentagon on October 5, General John F. Campbell said, "Afghan forces advised that they were taking fire from enemy positions and asked for air support from U.S. forces."

"An air strike was then called to eliminate the Taliban threat and several civilians were accidentally struck," he added.

An initial U.S. statement said the air strike had been in response to threats against U.S. forces.

Campbell said the military will ensure transparency in investigating the incident.

MSF accused Washington of "discrepancies" in the accounts, saying, "Their description of the attack keeps changing -- from collateral damage, to a tragic incident, to now attempting to pass responsibility to the Afghanistan government. The reality is the U.S. dropped those bombs."

MSF says it has shut down its operations in Kunduz following the strike.

The medical charity also called for an independent investigation into what it described as a war crime.

"Under the clear presumption that a war crime has been committed, MSF demands that a full and transparent investigation into the event be conducted by an independent international body," MSF General Director Christopher Stokes said.

Stokes added that the bombardment continued for more than an hour early on October 3, even after U.S. and Afghan authorities were informed the hospital had been hit.

MSF has said Afghan and coalition troops were fully aware of the exact location of the hospital, having been given GPS coordinates of a facility that had been providing care for four years.

MSF said that, besides the 22 people who were killed -- 12 staff members and 10 patients -- 40 others were seriously injured in the air strikes.

It said some 105 patients and their caregivers, as well as more than 80 international and local MSF staff, were in the hospital at the time of the bombing.

MSF denied any militants were present in the facility.

Afghan officials have claimed that insurgents were using the hospital building as a position to target Afghan forces and civilians.

"These statements imply that Afghan and U.S. forces working together decided to raze to the ground a fully functioning hospital with more than 180 staff and patients inside because they claim that members of the Taliban were present," Stokes said.

"This amounts to an admission of a war crime," he said. "This utterly contradicts the initial attempts of the U.S. government to minimize the attack as 'collateral damage.'"

'Deepest Condolences'

MSF's hospital in Kunduz is the only medical facility in northeastern Afghanistan that can deal with major injuries.

Its closure, even temporarily, could have a devastating impact on civilians.

"The MSF hospital is not functional anymore. All critical patients have been referred to other health facilities and no MSF staff are working in our hospital," Kate Stegeman, a spokeswoman for the charity, told AFP.

Stegeman said she could not confirm whether the hospital will reopen.

Earlier, U.S. President Barack Obama offered his "deepest condolences" for what he called a "tragic incident."

Obama also said the Pentagon has launched a "full investigation" into the air strikes.

But MSF's Stokes said that "relying only on an internal investigation by a party to the conflict would be wholly insufficient."

Stokes has called for an independent investigation.

NATO earlier conceded U.S. forces may have been behind the bombing, after they launched a strike which they said was intended to target militants.

UN human rights chief Zeid Ra'ad al-Hussein also called for a full and transparent probe, noting that an air strike on a hospital "may amount to a war crime."